JP2020155328A - Membrane-electrode assembly for fuel cell and solid polymer fuel cell - Google Patents

Abstract

To provide a membrane-electrode assembly which has good power generation characteristics and is hard to deteriorate without deteriorating the characteristics of membrane-electrode assemblies, such as gas diffusion properties and drainage properties, by maintaining larger pores in a catalyst layer.SOLUTION: A membrane-electrode assembly for a fuel cell has a constitution where an anode catalyst layer and a cathode catalyst layer, each of which includes carbon particles carrying a catalyst, a polymer electrolyte and a fibrous material, hold a proton conducting polymer electrolyte membrane therebetween. In the membrane-electrode assembly, the anode catalyst layer and the cathode catalyst layer do not include a reinforcement member, and the Young's modulus of the total of the anode catalyst layer and the cathode catalyst layer in the plane direction is lower than the Young's modulus of the polymer electrolyte membrane in the plane direction and is 7 MPa or more and 140 MPa or less.SELECTED DRAWING: None

Description

The present invention relates to a membrane electrode assembly.

In recent years, fuel cells have been attracting attention as an effective solution to environmental problems and energy problems. A fuel cell is a power generation device that oxidizes a fuel such as hydrogen using an oxidizing agent such as oxygen and converts the chemical energy associated therewith into electrical energy.
Fuel cells are classified into alkaline type, phosphoric acid type, polymer type, molten carbonate type, solid oxide type and the like according to the type of electrolyte. Polymer electrolyte fuel cells (PEFCs) are expected to be applied as portable power sources, household power sources, and in-vehicle power sources because they operate at low temperatures, have high output densities, and can be miniaturized and lightweight. There is.

The polymer electrolyte fuel cell (PEFC) has a structure in which a polymer electrolyte membrane, which is an electrolyte membrane, is sandwiched between a fuel electrode (anode) and an air electrode (cathode), and fuel gas and air containing hydrogen on the fuel electrode side. By supplying an oxidant gas containing oxygen to the electrode side, power is generated by the following electrochemical reaction.
_{^{Anode: H 2 → 2H + + 2e}} - ··· (1)
^{_{Cathode: 1 / 2O 2 + 2H +}} + 2e - → H 2 O ··· (2)

The anode and cathode each have a laminated structure of a catalyst layer and a gas diffusion layer. The fuel gas supplied to the anode-side catalyst layer becomes protons and electrons by the electrode catalyst (reaction 1). Protons move to the cathode through the polymer electrolyte and the polymer electrolyte membrane in the anode-side catalyst layer. The electrons pass through an external circuit and move to the cathode. In the cathode-side catalyst layer, protons, electrons, and an oxidant gas supplied from the outside react to generate water (reaction 2). In this way, electrons generate electricity by passing through an external circuit.
Examples of applications of fuel cells include mounting on automobiles as an in-vehicle power source. At this time, the membrane electrode assembly deteriorates due to cracks and the like due to the usage environment such as a desert area and a wet area, and the drying and swelling of the membrane electrode assembly due to the operation of the fuel cell.

Japanese Patent No. 6278932

As a method for solving the above problems, Patent Document 1 proposes a method for increasing the Young's modulus of the catalyst layer. As a method thereof, a fluorine-based proton-conducting polymer electrolyte membrane (PEM) is sandwiched between a fuel electrode and an air electrode, and then hot-pressed at a temperature higher than that of the conventional one to prepare a membrane electrode assembly. However, in this method, although small pores having a diameter of 10-50 nm are maintained, the polymer electrolyte is melted by hot pressing at a high temperature, and larger pores having a diameter of 100 nm or more in the catalyst layer are formed. It will be crushed. Since the large pores are crushed and only the small pores through which gas and water do not easily pass remain, the gas diffusivity and drainage property are deteriorated, and the power generation characteristics are deteriorated due to flooding.

Furthermore, crystallization of the polymer electrolyte by hot pressing at a high temperature reduces the conductivity of protons, causing a decrease in power generation characteristics.
Further, in Patent Document 1, in addition, the ion exchange capacity (IEC) of the polymer electrolyte is lowered, and the fluoropolymer electrolyte is changed to a polymer electrolyte such as polyarylene or PEEK (polyether ether ketone). Although it has been proposed to do so, the polymer electrolyte has a great influence on the power generation characteristics, so that the compatibility with the power generation characteristics is not sufficiently achieved.
The present invention has been made to solve the above-mentioned problems, and by maintaining the larger pores of the catalyst layer, the characteristics of the membrane electrode assembly such as gas diffusibility and drainage are not deteriorated. An object of the present invention is to provide a membrane electrode assembly having good power generation characteristics and which is not easily deteriorated.

In order to solve the above problems, the membrane electrode assembly for a polymer fuel cell according to one aspect of the present invention contains an anode catalyst layer and a cathode containing carbon particles carrying a catalyst, a polymer electrolyte, and a fibrous substance. It is a membrane electrode assembly for a fuel cell having a structure in which a proton-conducting polymer electrolyte membrane is sandwiched between catalyst layers, and the total plane-direction Young ratio of the anode catalyst layer and the cathode catalyst layer is the polymer. It is characterized in that it is lower than the Young ratio in the plane direction of the electrolyte membrane and is 7 MPa or more and 140 MPa or less. The "young rate in the plane direction of the total of the anode catalyst layer and the cathode catalyst layer" is a model in which the anode catalyst layer and the cathode catalyst layer are combined as described in [Method for calculating the young rate] described later. The calculated Young rate.

In the membrane electrode assembly for a fuel cell according to one aspect of the present invention, the fibrous substance can be carbon fiber.
Further, in the membrane electrode assembly for a fuel cell according to one aspect of the present invention, the Young's modulus of the anode catalyst layer is preferably higher than the Young's modulus of the cathode catalyst layer.
Further, in the membrane electrode assembly for a fuel cell according to one aspect of the present invention, the polymer electrolyte is preferably contained 1.0 times or more with respect to the mass of the fibrous substance.
Further, in the membrane electrode assembly for a fuel cell according to one aspect of the present invention, the fibrous substance is 0.1 times or more and 2.0 times or less the mass of the carbon particles excluding the mass of the catalyst. It is preferably contained.
The polymer electrolyte fuel cell according to another aspect of the present invention is a polymer electrolyte fuel cell having a membrane electrode assembly for a fuel cell according to the above aspect.

According to one aspect of the present invention, it is possible to provide a membrane electrode assembly for a polymer electrolyte fuel cell that has both high power generation characteristics and high durability.

It is sectional drawing which shows the structural example of the membrane electrode assembly which concerns on embodiment of this invention. It is a schematic diagram which shows the structural example of the catalyst layer which concerns on embodiment of this invention. It is a schematic diagram which shows the method example of the tensile strength test of the membrane electrode assembly which concerns on embodiment of this invention. It is an exploded perspective view which shows the structural example of the single cell of the polymer electrolyte fuel cell equipped with the membrane electrode assembly which concerns on embodiment of this invention.

Hereinafter, the present invention will be described in detail. It should be noted that the present invention is not limited to each of the embodiments described below, and modifications such as design changes can be made based on the knowledge of those skilled in the art, and such modifications are added. Such embodiments are also included in the scope of the present invention.
As shown in FIG. 1, the membrane electrode assembly 12 for a polymer electrolyte fuel cell according to the embodiment of the present invention (hereinafter, the present embodiment) is also referred to as a cathode catalyst layer 2 (hereinafter, simply referred to as “catalyst layer 2”). ) And the anode catalyst layer 3 (hereinafter, also simply referred to as “catalyst layer 3”) sandwich the proton-conducting polymer electrolyte membrane 1, and the total plane-wise young ratio of the catalyst layers 2 and 3 is formed. (Hereinafter, also referred to as “the Young ratio of the catalyst layers 2 and 3) is lower than the Young ratio in the plane direction of the polymer electrolyte membrane 1 and is 7 MPa or more and 140 MPa or less.

As shown in FIG. 2, the catalyst layers 2 and 3 for a polymer electrolyte fuel cell according to the present embodiment include carbon particles 14 carrying a catalyst 13, a polymer electrolyte 15, and a fibrous substance 16. By including the fibrous substance 16, cracks do not occur during formation, and larger pores in the catalyst layers 2 and 3 can be increased.
When the Young's modulus of the catalyst layers 2 and 3 is in the above range of 7 MPa or more and 140 MPa or less, cracks are less likely to occur in the catalyst layers 2 and 3 during fuel cell operation, and sufficiently high durability can be provided. If Young's modulus is less than 7 MPa, durability may be low. Further, when the Young's modulus of the catalyst layers 2 and 3 is in the above range, a large amount of larger pores in the catalyst layers 2 and 3 are present, so that sufficiently high power generation performance can be provided. When the Young's modulus is higher than 140 MPa, the polymer electrolyte 15 in the catalyst layers 2 and 3 crystallizes, or the substances in the catalyst layers 2 and 3 are firmly adhered to each other, and the catalyst layer density becomes high. When the polymer electrolyte crystallizes, the proton conductivity decreases, and the power generation performance may decrease. Further, when the catalyst layer density is high, the number of pores is reduced, the drainage property and the gas diffusibility are lowered, flooding is likely to occur, which may cause a deterioration in power generation performance.

As shown in FIG. 3, in the tensile strength test according to the present embodiment, one end of the membrane electrode assembly having the above configuration is fixed to the upper air jaw 17, and the other end is fixed to the lower air jaw 18, and the upper portion is described. This was carried out by raising the air jaw 17 at a speed of 100 mm / min. Further, the tensile strength in the plane direction refers to the tensile strength obtained by this measurement. When the cross section of the membrane electrode assembly 12 composed of the cathode catalyst layer 2 / the polymer electrolyte film 1 / the anode catalyst layer 3 shown in FIG. 1 is defined as the thickness direction, the direction perpendicular to the thickness direction is defined as the plane direction. ..

FIG. 4 is an exploded perspective view showing a configuration example of a single cell 11 of a polymer electrolyte fuel cell equipped with a membrane electrode assembly 12. As shown in FIG. 4, the air electrode side gas diffusion layer 4 and the fuel electrode side gas diffusion layer 5 face each other of the air electrode side electrode catalyst layer 2 and the fuel electrode side electrode catalyst layer 3 of the membrane electrode assembly 12, respectively. It is arranged. As a result, the air pole 6 and the fuel pole 7 are configured, respectively. Then, the air electrode 6 and the fuel electrode 7 are sandwiched by a set of separators 10 to form a single cell 11. The set of separators 10 is made of a conductive and gas impermeable material, and is a gas flow path for reaction gas flow arranged facing the air electrode side gas diffusion layer 4 or the fuel electrode side gas diffusion layer 5. 8 and a cooling water flow path 9 for cooling water flow arranged on the main surface facing the gas flow path 8 are provided.
In the single cell 11, an oxidizing agent such as air or oxygen is supplied to the air electrode 6 through the gas flow path 8 of one separator 10, and the fuel gas containing hydrogen passes through the gas flow path 8 of the other separator 10. Alternatively, organic fuel is supplied to the fuel electrode 7 to generate power.

The polymer electrolyte membrane (PEM) 1 is formed of, for example, a polymer material having proton conductivity, and examples of the polymer material having proton conductivity include a fluorine-based resin and a hydrocarbon-based resin. Can be mentioned. As the fluorine-based resin, for example, Nafion (manufactured by DuPont, registered trademark), Flemion (manufactured by Asahi Glass, registered trademark), Gore-Select (manufactured by Gore, registered trademark) and the like can be used. Examples of the hydrocarbon resin include engineering plastics and those in which a sulfonic acid group is introduced into a copolymer thereof. Among them, those having a Young's modulus of 200 MPa or more are preferable. When the Young's modulus of PEM1 is as low as 100 MPa or less, which is lower than the Young's modulus of the catalyst layers 2 and 3, the Young's modulus of the membrane electrode assembly becomes low. As a result, PEM1 tends to stretch even with a small stress, cracks easily occur in the catalyst layers 2 and 3, and the durability may decrease.

The polymer electrolyte 15 is, for example, a polymer substance having proton conductivity, and examples of the polymer substance having proton conductivity include a fluorine-based resin and a hydrocarbon-based resin. As the fluorine-based resin, for example, Nafion (manufactured by DuPont, registered trademark) or the like can be used. As the hydrocarbon resin, for example, engineering plastics or those in which a sulfonic acid group is introduced into a copolymer thereof can be used. By increasing the mass added, the Young's modulus of the catalyst layers 2 and 3 can be increased.

The dry mass value (equivalent weight; EW) per mole of the proton donating group of the polymer electrolyte 15 is preferably 400 to 1200, and more preferably 600 to 1000. If the EW is too small, the power generation performance may be lowered due to flooding, and if the EW is too large, the proton conductivity may be lowered and the power generation performance may be lowered.
The catalyst 13 includes, for example, platinum group elements such as platinum, palladium, ruthenium, iridium, rhodium, and osmium, as well as metals such as iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum. Alternatively, these alloys, oxides, compound oxides, etc. can be used. Among them, platinum and platinum alloy are preferable. Further, the particle size of these catalysts 13 is preferably 0.5 to 20 nm because if it is too large, the activity of the catalyst decreases, and if it is too small, the stability of the catalyst decreases. More preferably, 1 to 5 nm is preferable.

The carbon particles 14 may be any particles as long as they are fine particles, have conductivity, and are not affected by the catalyst 13. If the particle size of the carbon particles 14 is too small, it becomes difficult to form an electron conduction path, and if it is too large, the electrode catalyst layers 2 and 3 become thick and the resistance increases, which may reduce the output characteristics. Therefore, the average particle size of the carbon particles 14 is preferably about 10 to 1000 nm. More preferably, 10 to 100 nm is preferable.
It is preferable that the catalyst 13 is supported on the carbon particles 14. By supporting the catalyst 13 on the carbon particles 14 having a high surface area, the catalyst 13 can be supported at a high density, and the catalytic activity can be improved.

If the mass ratio (polymer electrolyte (I) / carbon particles (C)) of the polymer electrolyte 15 contained in the cathode catalyst layer 2 to the carbon particles 14 is too small, the proton diffusion rate will decrease and the power generation performance will decrease. , Young rate may also be low. On the other hand, if it is too large, the power generation performance may deteriorate due to flooding. Therefore, the mass ratio (I / C) is preferably 0.4 to 1.6, more preferably 0.5 to 1.3.
If the mass ratio of the polymer electrolyte 15 contained in the anode catalyst layer 3 to the carbon particles 14 (polymer electrolyte (I) / carbon particles (C)) is too small, the proton diffusion rate will decrease and the power generation performance will decrease. , Young rate may also be low. On the other hand, if it is too large, the power generation performance may deteriorate due to flooding. Therefore, the mass ratio (I / C) is preferably 0.5 to 1.5, more preferably 0.7 to 1.2.

As the fibrous substance 16, for example, carbon fiber, carbon nanofiber, carbon nanotube, cellulose nanofiber, chitin nanofiber, ceramics fiber, and polymer electrolyte fiber can be used. Preferred examples include carbon nanofibers and carbon nanotubes. By using the fibrous substance, it is possible to suppress an increase in electron transfer resistance in the catalyst layers 2 and 3.
The fibrous material 16 may be an electrode active material for an oxygen reducing electrode processed into a fibrous form, and for example, at least one transition metal element selected from Ta, Nb, Ti, and Zr may be used. Substances containing may be used. Examples thereof include partial oxides of carbonitrides of these transition metal elements, and conductive oxides and conductive oxynitrides of these transition metal elements.

Further, the fibrous substance 16 according to the present embodiment may be a polymer electrolyte having proton conductivity processed into a fibrous form, and for example, a fluorine-based polymer electrolyte or a hydrocarbon-based polymer electrolyte may be used. Can be used. As the fluorine-based polymer electrolyte, for example, Nafion (registered trademark) manufactured by DuPont, Flemion (registered trademark) manufactured by Asahi Glass Co., Ltd., AGClex (registered trademark) manufactured by Asahi Kasei Co., Ltd., Gore Select (registered trademark) manufactured by Gore, etc. are used. Can be done. As the hydrocarbon-based polymer electrolyte, for example, an electrolyte such as a sulfonated polyether ketone, a sulfonated polyether sulfone, a sulfonated polyether ether sulfone, a sulfonated polysulfide, or a sulfonated polyphenylene can be used. Above all, a Nafion (registered trademark) -based material manufactured by DuPont can be preferably used as the polymer electrolyte. As the hydrocarbon-based polymer electrolyte, for example, an electrolyte such as a sulfonated polyether ketone, a sulfonated polyether sulfone, a sulfonated polyether ether sulfone, a sulfonated polysulfide, or a sulfonated polyphenylene can be used.

The fiber diameter of the fibrous substance 16 is preferably 0.5 to 500 nm, more preferably 10 to 300 nm. By setting the above range, the number of pores in the catalyst layers 2 and 3 can be increased, and high output can be achieved.
The fiber length of the fibrous substance 16 is preferably 1 to 200 μm, more preferably 1 to 50 μm. By setting the fiber length to 1 μm or more, the Young's modulus of the catalyst layers 2 and 3 can be increased, and cracks can be suppressed during formation or operation of the fuel cell. In addition, larger pores in the catalyst layers 2 and 3 can be increased, which may lead to higher output. If the fiber length is too long, fiber agglomeration may occur and the output may decrease.

The fibrous substance 16 contained in the catalyst layers 2 and 3 is preferably contained in an amount of 0.1 to 2.0 times the mass of the carbon particles 14 excluding the mass of the catalyst 13. If the content is too small, the Young's modulus of the catalyst layers 2 and 3 is significantly lowered, and if it is too high, the power generation performance may be lowered.
The polymer electrolyte 15 is preferably contained 1.0 times or more, preferably 1.0 to 8.0 times the mass of the fibrous substance 16. If the content is too small, the polymer electrolyte 15 around the catalyst 13 is reduced and the power generation performance is lowered, and if the content is too high, the power generation performance may be lowered due to flooding.

It is preferable that the mass of the fibrous substance 16 contained in the anode catalyst layer 3 is larger than the mass of the fibrous substance 16 contained in the cathode catalyst layer 2. This is because the increase in mass of the fibrous substance 16 in the anode catalyst layer 3 has a smaller effect on the power generation characteristics than the increase in mass of the fibrous substance 16 in the cathode catalyst layer 2. By increasing the mass of the fibrous substance 16 contained in the catalyst layers 2 and 3, the Young's modulus of the catalyst layers 2 and 3 may increase. As the Young's modulus of the catalyst layers 2 and 3 increases, the Young's modulus of the membrane electrode assembly increases.

That is, as a method for increasing the Young's modulus of the catalyst layers 2 and 3, it was recommended to add a large amount of the polymer electrolyte 15 and the fibrous substance 16 and to increase the fiber length of the fibrous substance 16 to be added. However, if the Young's modulus of the catalyst layers 2 and 3 exceeds 200 MPa or the like, and the Young's modulus becomes higher than that of PEM1, the power generation performance may be deteriorated. Therefore, the Young's modulus of the catalyst layers 2 and 3 needs to be lower than the Young's modulus of PEM1.
The thickness of the catalyst layers 2 and 3 for the polymer fuel cell is preferably 20 μm or less, more preferably 10 μm. If the thickness is larger than 20 μm, the resistance of the catalyst layers 2 and 3 becomes large, and the output may decrease.

(Manufacturing method of catalyst layer)
The catalyst layers 2 and 3 for a polymer fuel cell can be produced by preparing a slurry for a catalyst layer, coating and drying it on a base material or the like.
The catalyst layer slurry is composed of a catalyst 13, carbon particles 14, a polymer electrolyte 15, a fibrous substance 16, and a solvent. The solvent is not particularly limited, but a solvent capable of dispersing or dissolving a polymer electrolyte is preferable. Commonly used solvents include, for example, water, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, alcohols such as tert-butyl alcohol, acetone, methyl ethyl ketone, methyl. Ketones such as propyl ketone, methyl butyl ketone, methyl isobutyl ketone, methyl amyl ketone, pentanone, heptanone, cyclohexanone, methylcyclohexanone, acetonyl acetone, diethyl ketone, dipropyl ketone, diisobutyl ketone, tetrahydrofuran, tetrahydropyran, dioxane, Diethylene glycol dimethyl ether, anisole, methoxytoluene, diethyl ether, dipropyl ether, dibutyl ether and other ethers, isopropylamine, butylamine, isobutylamine, cyclohexylamine, diethylamine, aniline and other amines, propyl forate, isobutyl foreate, amyl forate, Esters such as methyl acetate, ethyl acetate, propyl acetate, butyl acetate, isobutyl acetate, pentyl acetate, isopentyl acetate, methyl propionate, ethyl propionate, butyl propionate, and other esters such as acetic acid, propionic acid, dimethylformamide, dimethylacetamide, N -Methylpyrrolidone or the like may be used. Examples of glycol and glycol ether solvents include ethylene glycol, diethylene glycol, propylene glycol, ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diacetone alcohol, 1-methoxy-2-propanol and 1-ethoxy. -2-Propanol and the like can be mentioned.

The solid content concentration of the slurry for the catalyst layer is about 5 to 30% by mass, preferably about 8 to 20% by mass. If the concentration is too small, the viscosity of the slurry decreases and the coating amount cannot be made constant, and if the concentration is too large, the viscosity of the slurry increases and the appearance of the coated catalyst layers 2 and 3 may deteriorate.
Examples of the method for applying the slurry for the catalyst layer include, but are not limited to, a doctor blade method, a die coating method, a dipping method, a screen printing method, a laminator roll coating method, and a spray method.
Examples of the method for drying the slurry for the catalyst layer include warm air drying and IR drying. The drying temperature is about 40 to 200 ° C., preferably about 40 to 120 ° C. If the drying temperature is too low, the solvent will not volatilize, and if it is too high, there is a risk that the slurry for the catalyst layer will ignite.
The drying time of the catalyst layer slurry is about 0.5 minutes to 1 hour, preferably about 1 minute to 30 minutes. If the drying time is too short, the solvent may remain, and if it is too long, the polymer electrolyte membrane 1 may be deformed due to drying.

(Manufacturing method of membrane electrode assembly)
As a method for producing the membrane electrode assembly 12, for example, the catalyst layers 2 and 3 are formed on the transfer base material or the gas diffusion layers 4 and 5, and then the catalyst layers 2 and 3 are formed on the polymer electrolyte membrane 1 by thermal pressure bonding. The method of forming the catalyst layers 2 and 3 directly on the polymer electrolyte membrane 1 can be mentioned. The method of directly forming the catalyst layers 2 and 3 on the polymer electrolyte membrane 1 is preferable because the adhesion between the polymer electrolyte membrane 1 and the catalyst layers 2 and 3 is high and the catalyst layers 2 and 3 are not likely to be crushed.

Next, an example based on the present invention will be described.
[Tensile strength test]
Young's modulus was measured by a tensile strength test using a Tensilon universal material tester (RTG-1250A, A & D). The test piece was prepared as follows. The membrane electrode assembly 12 having the catalyst layers 2 and 3 of 50 mm square was cut out in a direction parallel to or perpendicular to the machine direction of PEM1 (machine direction) or a direction perpendicular to the machine direction (transdirection) to a length of about 50 mm and a width of 10 mm. By setting the distance between the upper air jaw 17 and the lower air jaw 18 that fix the upper and lower parts of the test piece to 30 mm, the length L of the original material was kept constant at 30 mm. A tensile test was performed at a speed of 100 mm / min. The measurement was performed indoors at 25 degrees Celsius.

[Calculation of Young's modulus]
A method of calculating Young's modulus in the plane direction will be described.
(1) For PEM1, stress was applied in the plane direction by the tensile test, the amount of strain at this time was measured, and Young's modulus was calculated based on the stress and strain.
(2) For the cathode catalyst layer 2 and the anode catalyst layer 3, it is difficult to directly measure the Young's modulus in the plane direction. Therefore, the total Young's modulus of PEM1 and the catalyst layers 2 and 3 was measured, and the Young's modulus was calculated by calculation. In this calculation, the target Young's modulus is calculated assuming an equivalent model in which the PEM1 and the catalyst layers 2 and 3 are regarded as parallel springs.
(3) Young's modulus E can be expressed by E = PL / Aλ using the load P, the original length L of the material, the original cross section A of the material, and the deformation amount λ. Using the original width W of the material and the original thickness T of the material, it can be expressed as A = WT. Here, when the original width W of the material is constant, Young's modulus E is inversely proportional to the thickness T of the material.

(4) Young's modulus _{E CAT} catalyst layers 2 and 3, the Young's modulus _{E PEM} of the measured PEM1, the thickness _{T PEM} Young's modulus _E MEA, PEM1 the measured membrane electrode assembly 12, the cathode catalyst layer 2 and anode catalyst Using the total _TCAT of the thickness of layer 3,
E _CAT = {E _MEA x (T _PEM + T _CAT ) -E _PEM x T _PEM } / T _CAT
It was calculated as.
(5) Total Thickness of Cathode Catalyst Layer 2 and Anode Catalyst Layer 3 T _CAT and PEM Thickness The T _PEM was calculated from the cross-sectional SEM image of the membrane electrode assembly 12.
(6) Young's modulus E _{PEM of} PEM1 and Young's modulus E _MEA of the membrane electrode assembly 12 have different values depending on the machine direction and transdirection of PEM1. E _PEM and E _MEA were averaged values in each direction.
(7) When measuring only the Young's modulus of the cathode catalyst layer 2 or the anode catalyst layer 3, the tensile strength of the membrane electrode assembly coated with these catalyst layers 2 or 3 on only one side of PEM1 is measured. , Young's modulus was calculated.

[Evaluation of power generation performance]
A gas diffusion layer (SIGRACET (R) 35BC, manufactured by SGL) was arranged outside the catalyst layers 2 and 3, and the power generation characteristics were evaluated using a commercially available JARI standard cell. The cell temperature was set to 80 ° C., and hydrogen (100% RH) was supplied to the anode and air (100% RH) was supplied to the cathode for evaluation.

[Evaluation of durability]
A gas diffusion layer (SIGRACET (R) 35BC, manufactured by SGL) is placed outside the catalyst layers 2 and 3, and a humidity cycle test is performed using a commercially available JARI standard cell to determine the susceptibility of the membrane electrode assembly to deterioration. By investigating, the durability was evaluated. This evaluation was carried out according to the durability evaluation protocol (cell evaluation analysis protocol, December 2012) established by the New Energy and Industrial Technology Development Organization. The cell temperature was 80 ° C., nitrogen was supplied to the anode and the cathode, and the humidity was 150% RH and 0% RH, which were maintained for 2 minutes each. When the leak current value became 10 times or more the initial leak current value, it was determined that the membrane electrode assembly had deteriorated.

[Example 1]
Take 20 g of platinum-supported carbon (TEC10E50E, manufactured by Tanaka Kikinzoku Co., Ltd.) in a container, add 150 g of water and mix, then 150 g of 1-propanol, 10 g of polymer electrolyte (Nafion® dispersion, Wako Pure Chemical Industries, Ltd.) and fibrous. As a substance, 5 g of carbon nanofiber (manufactured by Showa Denko Co., Ltd., trade name "VGCF-H", fiber diameter of about 150 nm, fiber length of about 10 μm) was added and stirred to produce a slurry for a cathode catalyst layer. Of the 20 g of platinum-supported carbon used in this example, the carbon component was 10 g.
Take 20 g of platinum-supported carbon (TEC10E50E, manufactured by Tanaka Kikinzoku Co., Ltd.) in a container, add 150 g of water and mix, then 150 g of 1-propanol, 15 g of polymer electrolyte (Nafion® dispersion, Wako Pure Chemical Industries, Ltd.) and fibrous. 15 g of carbon nanofiber (manufactured by Showa Denko Co., Ltd., trade name "VGCF-H", fiber diameter of about 150 nm, fiber length of about 10 μm) was added as a substance and stirred to produce a slurry for an anode catalyst layer.
The obtained cathode catalyst layer slurry and anode catalyst layer slurry are coated on a polymer electrolyte membrane (PEM) (Dupont, Nafion212) by a die coating method and dried in a furnace at 80 ° C. to obtain a high value. A membrane electrode assembly for a molecular fuel cell was manufactured.

[Example 2]
Take 20 g of platinum-supported carbon (TEC10E50E, manufactured by Tanaka Kikinzoku Co., Ltd.) in a container, add 150 g of water and mix, then 150 g of 1-propanol, 8 g of polymer electrolyte (Nafion® dispersion, Wako Pure Chemical Industries, Ltd.) and fibrous. As a substance, 10 g of carbon nanofiber (manufactured by Showa Denko Co., Ltd., trade name "VGCF-H", fiber diameter of about 150 nm, fiber length of about 10 μm) was added and stirred to produce a slurry for a catalyst layer. Of the 20 g of platinum-supported carbon used in this example, the carbon component was 10 g.
The obtained catalyst layer slurry is coated on both sides of PEM (Nafion212 manufactured by Dupont Co., Ltd.) by a die coating method and dried in a furnace at 80 ° C. to manufacture a membrane electrode assembly for a polymer fuel cell. did.

[Example 3]
The fibrous material is coated with 2 g of carbon nanotubes (manufactured by Nanocil, trade name "NC7000", fiber diameter of about 9.5 nm, fiber length of about 1.5 μm), and polymerized by the same procedure as in Example 2. A membrane electrode assembly for a fuel cell was manufactured.
[Example 4]
For polymer fuel cells, the procedure is the same as in Example 2 except that 3 g of cellulose nanofibers (fiber diameter: about 4 nm, fiber length: about 300 nm) produced from coniferous kraft pulp by a known method is used as the fibrous substance. A membrane electrode assembly was manufactured.
[Example 5]
A membrane electrode assembly for a polymer fuel cell was produced in the same procedure as in Example 2 except that the amount of the fibrous substance added was changed to 1 g.
[Example 6]
A membrane electrode assembly for a polymer fuel cell was produced in the same procedure as in Example 2 except that the amount of the polymer electrolyte added was changed to 10 g.

[Example 7]
Take 20 g of platinum-supported carbon (TEC10E50E, manufactured by Tanaka Kikinzoku Co., Ltd.) in a container, add 150 g of water and mix, then 150 g of 1-propanol, 10 g of polymer electrolyte (Nafion® dispersion, Wako Pure Chemical Industries, Ltd.) and fibrous. As a substance, 5 g of carbon nanofiber (manufactured by Showa Denko Co., Ltd., trade name "VGCF-H", fiber diameter of about 150 nm, fiber length of about 10 μm) was added and stirred to obtain a catalyst layer slurry 5. Of the 20 g of platinum-supported carbon used in this example, the carbon component was 10 g.
The obtained catalyst layer slurry was applied to a PET film by a die coating method and dried in a furnace at 80 ° C. to obtain a catalyst layer. Two of the above catalyst layers were manufactured, and a polymer electrolyte membrane (DuPont, Nafion212) was sandwiched between them and transferred from both sides by hot pressing at 100 degrees Celsius to manufacture a membrane electrode assembly for a polymer electrolyte fuel cell. ..

[Comparative Example 1]
A membrane electrode assembly for a polymer fuel cell was produced in the same procedure as in Example 2 except that 5 g of a plate-like substance graphene (thickness: about 15 μm, width: about 5 μm) was added instead of the fibrous substance.
[Comparative Example 2]
As the fibrous substance, a polymer fuel cell was prepared in the same procedure as in Example 2 except that 0.5 g of cellulose nanofibers (fiber diameter: about 4 nm, fiber length: about 300 nm) produced from coniferous kraft pulp by a known method was used. A membrane electrode assembly for a battery was manufactured.
[Comparative Example 3]
A membrane electrode assembly for a polymer fuel cell was produced in the same procedure as in Example 2 except that no fibrous substance was added.
[Comparative Example 4]
A membrane electrode assembly for a polymer fuel cell was produced in the same procedure as in Example 2 except that the amount of the fibrous substance added was changed to 30 g.

[Comparative Example 5]
A membrane electrode assembly for a polymer fuel cell was produced in the same procedure as in Example 7 except that no fibrous substance was added.
[Comparative Example 6]
A membrane electrode assembly for a polymer fuel cell was manufactured by the same procedure as in Comparative Example 5 except that the hot press temperature was changed to 160 degrees Celsius.
[Comparative Example 7]
A membrane electrode assembly for a polymer fuel cell was manufactured by the same procedure as in Example 2 except that the PEM used was changed to one having a low Young's modulus.
With respect to the membrane electrode assemblies of Examples 1 to 7 and Comparative Examples 1 to 7, Young's modulus was measured and power generation characteristics and durability were evaluated. The results are shown in Table 1. In Examples 1 to 7 and Comparative Examples 1 to 6, the Young's modulus E _PEM of _PEM is 200 MPa. In Comparative Example 7, the Young's modulus E _PEM of _PEM is 100 MPa.

As shown in Table 1, in the membrane electrode assembly, when the Young's modulus of the catalyst layer was 7 to 140 MPa, both the power generation characteristics and the durability were high. When the Young's modulus of the catalyst layer was less than 7 MPa, the durability tended to be low. This is because the Young's modulus of the catalyst layer is low, so that the Young's modulus of the membrane electrode assembly is low, and as a result of the large dimensional change in the durability evaluation test, the catalyst layer is likely to crack. it is conceivable that. On the other hand, when the Young's modulus of the catalyst layer was higher than 140 MPa, the power generation characteristics tended to be low. It is considered that this is because the composition of the catalyst layer changed significantly due to hot pressing at high temperature and the addition of a large amount of fibrous substance.

In Example 1, the Young's modulus of each of the cathode catalyst layer and the anode catalyst layer was also measured. As a result, the Young's modulus of the anode catalyst layer was higher than the Young's modulus of the cathode catalyst layer. This is because the weight of the fibrous substance relative to the weight of the carbon particles contained in the catalyst layer is heavier in the anode catalyst layer than in the cathode catalyst layer.
In Example 1, the Young ratio of the anode catalyst layer was made higher than that of the cathode catalyst layer, the weight of the fibrous substance was made 0.1 times or more with respect to the weight of the carbon particles contained in the catalyst layer, and the catalyst layer was contained. By increasing the weight of the polymer electrolyte to 1.0 times or more the weight of the fibrous material contained, a membrane electrode assembly exhibiting the highest power generation characteristics and high durability was obtained.

In Example 6, the Young's modulus of the catalyst layer was increased by increasing the weight of the polymer electrolyte with respect to the weight of the fibrous substance contained in the catalyst layer as compared with Example 2, and the Young's modulus of the catalyst layer was increased. Durability was improved in comparison.
In Comparative Example 7, since the Young's modulus of PEM was lower than the Young's modulus of the catalyst layer, the durability was significantly reduced.
As described above, according to the present embodiment, the Young's modulus of the catalyst layer of the membrane electrode assembly can be optimized. This makes it possible to provide a catalyst layer for a polymer fuel cell that exhibits high power generation characteristics and high durability.

1 Polymer electrolyte film 2 Cathode catalyst layer 3 Anode catalyst layer 4 Cathode side gas diffusion layer 5 Anode side gas diffusion layer 6 Anode 7 Anode 8 Gas flow path 9 Cooling water flow path 10 Separator 11 Single cell 12 Film electrode junction 13 Catalyst 14 Carbon Particle 15 Polymer Electrolyte 16 Fibrous Material 17 Upper Air Jaw 18 Lower Air Jaw

Claims (6)

A membrane electrode assembly for a fuel cell having a structure in which a proton-conducting polymer electrolyte membrane is sandwiched between an anode catalyst layer and a cathode catalyst layer containing carbon particles carrying a catalyst, a polymer electrolyte, and a fibrous substance. The fuel cell is characterized in that the total plane-direction Young ratio of the anode catalyst layer and the cathode catalyst layer is lower than the plane-direction Young ratio of the polymer electrolyte membrane, and is 7 MPa or more and 140 MPa or less. Membrane electrode assembly. The membrane electrode assembly according to claim 1, wherein the fibrous substance is carbon fiber. The membrane electrode assembly according to claim 1 or 2, wherein the Young's modulus of the anode catalyst layer is higher than the Young's modulus of the cathode catalyst layer. The membrane electrode assembly according to any one of claims 1 to 3, wherein the polymer electrolyte is contained 1.0 times or more with respect to the mass of the fibrous substance. Any one of claims 1 to 3, wherein the fibrous substance is contained in an amount of 0.1 times or more and 2.0 times or less with respect to the mass of the carbon particles excluding the mass of the catalyst. The membrane electrode assembly according to the item. A polymer electrolyte fuel cell having the membrane electrode assembly according to any one of claims 1 to 5.

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